This invention relates to equipment for plasma processing semiconductor wafers and, in particular, to a pin lift mechanism which can be incorporated into an electrode of said equipment.
In the prior art, such as disclosed in U.S. Pat. No. 4,632,624, three or more pins are used to raise a semiconductor wafer above an electrode in a plasma reactor. The pins extend through the electrode and are attached to a lift plate located beneath the electrode. The lift plate is enclosed in a small chamber. This chamber presents a problem in that it increases the volume which must be pumped and purged. It increases process times because it increases the volume of the system. The chamber further presents a problem in purging the system of unwanted gases since it presents a volume in which they can be trapped. In addition to possibly contaminating the gases in the reactor chamber proper, there is the difficulty of having reactive gases entering the chamber and possibly corroding materials therein.
In purely mechanical terms, a wafer pin lift represents a somewhat delicate mechanism and a source of particles due to the closeness of fit of the pins within their respective bores. The motion of the lift mechanism must be quite accurate to avoid misaligning the pins in the bores. Further, the pins are rigidly held in place while receiving a wafer; i.e. there is no give in the system to soften the contact between the wafer and the pins.
In view of the foregoing, it is therefore an object of the present invention to provide an improved pin lift mechanism for semiconductor wafers.
Another object of the present invention is to reduce the time necessary for pumping down and/or purging a plasma processing system having a lift pin assembly.
A further object of the present invention is to provide a pin lift mechanism having a compliant member.